Cracked Valve Seats and Pre-Cups

WarNose · Oct 17, 2018

Upon inspection, the machine shop says that between both heads there are 7 small cracks in the valve seats and each pre-chamber has multiple small cracks. He says the cracks aren't a super big deal and thinks that it would be hard to find 6.9 heads in better shape. What do you all think?

Thewespaul · Oct 17, 2018

Sounds like he’s dealt with idi heads before. Almost every idi precup I see is cracked, just make sure they don’t go past the fire ring, the valve seats can be an issue depending on how severe they are but it really depends on your machinest’s judgement.

genscripter · Oct 17, 2018

You must be registered for see images attach

Thewespaul · Oct 17, 2018

Only time I’ve seen it crack on the outside diameter of the precup is when a head gasket was blown from it lifting a head. The precup had room to drop down and flame front got around the edges.

IDIBRONCO · Oct 17, 2018

Your machinist does realize that the valve seats are replaceable, right? What's the big deal with bad seats?

Macrobb · Oct 17, 2018

No matter what you do, the engine will run. IDIs are amazingly tough, and things don't have to be perfect. Precups always crack. As long as you don't have any chance of coolant leaking through cracks in your head(or combusion gasses coming out), you should be OK...

WarNose · Oct 19, 2018

This thread shows why intake seats are not replaceable:

https://www.oilburners.net/threads/cavitation-check.71720/#post-834463

DrCharles · Oct 19, 2018

This may be a silly question, but could the seat inserts be coated with green Loctite or whatever they use on cylinder sleeves to retain them? If it's a tight press fit there shouldn't be a leak if the insert completely covered the hole into the water jacket.

IDIBRONCO · Oct 19, 2018

WarNose said:
This thread shows why intake seats are not replaceable:

https://www.oilburners.net/threads/cavitation-check.71720/#post-834463

Now I understand. Thanks.

WarNose · Oct 23, 2018

genscripter said:
You must be registered for see images attach

Does anyone have any idea about the chances of acceptable pre-cup cracks becoming unacceptable in the next 100,000 miles or so? Or valve seat cracks, for that matter?

Thewespaul · Oct 23, 2018

Will cali fall into the ocean tomorrow? Keep your egts below 1200* and dont overheat the engine is about all you can do. If I was doing the rebuild and the cracks were acceptable and you felt uneasy about them I would use a better set of heads. I wouldnt have any issue running cracked pre cups on my own trucks, but you want your customer to be completely at ease with their engine. Id say in your case if you feel you cant trust the heads the way they are now then pay the money now to make it right.

Cracked Valve Seats and Pre-Cups

WarNose

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Thewespaul

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genscripter

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Thewespaul

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IDIBRONCO

IDIBRONCO

Macrobb

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WarNose

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DrCharles

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IDIBRONCO

IDIBRONCO

WarNose

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Thewespaul

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